The left atrial appendage is the small conical projection from the upper anterior portion of the left atrium. Blood pooling in the appendage may arise spontaneously or as a result of atrial fibrillation. When blood pools in the appendage, blood clots can form. The migration of clots from the left atrial appendage to the bloodstream can cause serious problems when they embolize in the arterial system. More than 90% of clots formed during atrial fibrillation are formed in the left atrial appendage. Sievert et al., CIRCULATION 105:1887-1889 (2002). Embolization of these clots is a frequent cause of stroke. Thus, prevention of clot formation in, or clot migration from, the left atrial appendage may reduce the occurrences of stroke in patients with atrial fibrillation.
A common method of reducing the risk of clot formation is treatment with anticoagulants such as warfarin. Such treatment has been an effective method of reducing the incidence of stroke. However, strokes may still occur in patients using anticoagulants if there is a necessary or inadvertent lapse in treatment. Also, many patients who are at risk of stroke are contraindicated from using anticoagulants. Anticoagulant treatment is effective, but the difficulty in treating patients continuously and the high occurrence of contraindication give rise to a need for a different treatment option.
Another method of treatment designed to reduce clotting and embolization leading to stroke is left atrial appendage obliteration. Clearly, obliteration of the appendage will lead to less clotting during atrial fibrillation. Obliteration may occur during open cardiac surgery or via a less invasive thoracoscopic procedure. Many patients with a high risk of stroke are not candidates for such procedures because of their compromised health status. Further, obliteration of the left atrial appendage may have adverse haemodynamic and hormonal effects that have not been fully studied. See Al-Saady et al., HEART 82:547-554 (1999).
The limitations of anticoagulant treatment and surgical obliteration of the left atrial appendage give rise to the need for a less invasive method and device for aiding to prevent migration of clots from the left atrial appendage into the bloodstream.
Various devices have been developed and used for left atrial appendage occlusion. One such device includes a nitinol cage enclosed in an ePTFE membrane. The device is designed to be inserted entirely into the left atrial appendage and has multiple anchors for attachment to the interior wall of the left atrial appendage. Because the device is designed to be inserted entirely in the left atrial appendage, the device must be properly sized to ensure complete occlusion of the left atrial appendage. Improper measurement of the device may lead to increased implantation times or decreased effectiveness of the device if the wrong size is implanted.
Another device includes a wire cage partially covered by an ePTFE membrane. This device is also designed to be inserted entirely within the left atrial appendage and includes no anchors for attachment within the left atrial appendage. As above, improper measurement of this device may result in increased implantation times or decreased effectiveness. Also, the lack of an anchoring mechanism may lead to more serious complications if the device migrates out of the left atrial appendage.
Still another device used for left atrial appendage occlusion includes a double disk nitinol mesh designed to occlude by clamping to the opening of the left atrial appendage. This device does not include anchors for attaching to the musculature of the left atrial appendage and must be sized properly to prevent migration of the device out of the left atrial appendage. Again, improper measurement of the device may lead to increased implantation time or more serious complications.
Thus, the shortcomings of the prior art devices may lead to longer procedures, incomplete occlusion of the left atrial appendage, or serious complications triggered by migration of the device out of the left atrial appendage. Furthermore, conventional devices are oversized, potentially causing stretching of the left atrial appendage. For example, conventional devices may be oversized by 20-25%. Such stretching may lead to erosion or arrhythmia.